An important aspect of the manufacture of integrated circuits is the testing of an integrated circuit in order to verify that it operates according to specifications. Although the circuit could be tested after the integrated circuit has been packaged, the expense involved in dicing the wafer and packaging the individual integrated circuits makes it advantageous to test the integrated circuit as early as possible in the fabrication process so that unnecessary efforts will not be expended on faulty devices. It is therefore desirable that these circuits be tested either immediately after wafer fabrication is completed, and before separation into dice, or after dicing but before packaging. In either case, it is necessary to make electrical connection to all the circuit's external connections (usually bonding pads) in a nondestructive way, so as not to interfere with subsequent packaging and connection operations.
It is preferable that an integrated circuit be tested under its design operating conditions and to the extremes of its design performance range. In particular, typical high speed circuits are designed to operate with input and output signal bandwidths exceeding 1 GHz, and operation of such circuits should be evaluated at these high frequencies.
It has previously been proposed that an integrated circuit be tested using a probe comprising a body of elastomer having conductor runs of metals deposited on one face thereof. This probe is subject to a number of disadvantages. For example, the probe is not capable of supporting signals at frequencies above a few hundred megahertz without serious signal degradation, and it has poor mechanical stability owing to the large difference in elasticity of the elastomer body and the metallic conductor runs.
U.S. patent application Ser. No. 812,145 filed Dec. 23, 1985, the disclosure of which is hereby incorporated by reference herein, discloses a probe assembly for use in testing an integrated circuit. The probe assembly comprises a stiff support member formed with an aperture, and an elastically-deformable membrane. Both the support member and the membrane comprise dielectric material and portions of conductive material supported by the dielectric material in electrically-insulated relationship. The portions of conductive material of the membrane constitute inner contact elements distributed over a first main face of the membrane in a first pattern that corresponds to the pattern of contact areas on the contact face of the integrated circuit. Outer contact elements are distributed about a peripheral area of the membrane in a second pattern, and transmission lines extend from the inner contact elements to the outer contact elements respectively. The portions of conductive material of the support member comprise inner contact elements that are distributed about the aperture in a pattern corresponding generally to the second pattern, and transmission lines extending from the inner contact elements of the support member to testing apparatus. The membrane is secured to the support member so that it extends over the aperture, and the outer contact elements of the membrane are electrically connected to respective inner contact elements of the support member.
In a practical form of the probe assembly the support member is disposed horizontally in use, and the inner contact elements of the support member are exposed at the upper surface thereof. The outer contact elements of the membrane are exposed at the first main face of the membrane, and the membrane is clamped at its peripheral area to the upper surface of the support member using a body of elastomer material that spans the aperture in the support member. The first main face of the membrane is presented downwards, towards the interior of the aperture in the support member, and the integrated circuit is placed on a pedestal that is sufficiently small to enter the aperture in the support member. The body of elastomer material has a downwardly-projecting protuberance that engages the membrane directly above the inner contact elements, so that when the pedestal is raised, the contact areas of the integrated circuit engage the inner contact elements of the membrane, upward deformation of the membrane is resisted in a resiliently yieldable fashion and the body of elastomer material supplies contact force for achieving pressure contact between the contact areas of the integrated circuit and the inner contact elements of the membrane. The maximum linear dimension of the aperture in the support member is smaller than the diameter of a standard semiconductor wafer. Because the integrated circuit under test must be lifted into the aperture in the support member, the probe assembly is not well suited for testing integrated circuits in wafer form.
In U.S. patent application Ser. No. 904,600, filed Sept. 5, 1986, a probe suitable for testing integrated circuits in wafer form comprises a stiff support member formed with an aperture, and an elastically-deformable membrane. The membrane has first and second main faces, and is attached to the underside of the support member at its first main face so as to extend over the aperture. Both the support member and the membrane comprise dielectric material and portions of conductive material supported by the dielectric material in electrically-insulated relationship. The portions of conductive material of the membrane constitute inner contact elements exposed at the second main face of the membrane in a first pattern that corresponds to the pattern of contact areas on the contact face of the integrated circuit, outer contact elements distributed about a peripheral area of the first main face of the membrane in a second pattern, and transmission lines extending from the inner contact elements to the outer contact elements respectively. The portions of conductive material of the support member comprise inner contact elements on the underside of the support member that are distributed about the aperture in a pattern corresponding generally to the second pattern, and transmission lines extending from the inner contact elements of the support member to connectors for testing apparatus. The outer contact elements of the membrane are electrically connected to respective inner contact elements of the support member. The inner contact elements of the membrane each include a localized contact bump of conductive material, and the bumps project lower than any other parts of the probe that are at a distance from the contact bumps that is less than the diameter of the wafer containing the integrated circuit under test. Thus the contact bumps may engage bonding pads on an integrated circuit on a wafer situated below the support member.
In this probe assembly the membrane is soldered to the support member and cannot be easily replaced under typical field conditions. Consequently when the configuration of the integrated circuit to be tested changes, or when contact bumps on the membrane become worn, the entire probe assembly must be replaced.